A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:                a plurality of display electrode pairs disposed in parallel on a front glass substrate; and        a dielectric layer and a protective layer for covering the display electrode pairs.Here, each display electrode pair is formed of a pair of scan electrode and sustain electrode. The back plate has the following elements:        a plurality of data electrodes disposed in parallel on a back glass substrate;        a dielectric layer for covering the data electrodes;        a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and        phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon with a partial pressure of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color display.        
A subfield method is generally used as a method of driving the panel. In this method, one field period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display.
Each subfield has a setup period, an address period, and a sustain period. In the setup period, initializing discharge is performed to form a wall charge required for a subsequent addressing voltage on each electrode. The initializing operation includes an initializing operation (hereinafter referred to as “all-cell initializing operation”) of causing initializing discharge in all discharge cells, and an initializing operation (hereinafter referred to as “selection initializing operation”) of causing initializing discharge in a discharge cell having performed sustaining discharge.
In the address period, address pulse voltage is selectively applied to a discharge cell where display is to be performed, and addressing discharge is caused to form a wall charge (this operation is hereinafter referred to as “writing”). In the sustain period, sustain pulses are alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustaining discharge is caused in the discharge cell having performed addressing discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
Of the subfield method, a new driving method is disclosed. In this driving method, the initializing discharge is performed using a gently varying voltage waveform, and the initializing discharge is selectively applied to the discharge cell having performed sustaining discharge. Thus, light emission that is not related to the gradation display is minimized, and the contrast ratio is improved.
Specifically, in the setup period of one of a plurality of subfields, the all-cell initializing operation of causing discharge from all discharge cells is performed. In the setup period of another subfield, the selection initializing operation of initializing only the discharge cell having performed sustaining discharge is performed. As a result, light emission that is not related to the display is only the light emission accompanying the discharge of the all-cell initializing operation, and an image having sharp contrast can be displayed (e.g. patent document 1).
This driving manner allows image display of sharp contrast. That is because the luminance (hereinafter referred to as “black luminance”) in a black display region varying in response to the light emission that is not related to the image display is determined only by weak light emission in the all-cell initializing operation.
The definition and screen size of the panel have been recently increased, and hence the quality of display images has been required to be further improved.
Sharpening the contrast is one of the effective methods for improving the image quality. For instance, an attempt is made to further sharpen the contrast by reducing the light emitting luminance during the initializing discharge by reducing maximum voltage in the all-cell initializing operation.
When the maximum voltage in the all-cell initializing operation is reduced, however, priming generated during initialization decreases to cause strong discharge in the initializing operation in the next field, sustaining discharge occurs though writing has not been performed, and a discharge cell (hereinafter referred to as “initializing bright point”) that emits light can be generated disadvantageously. Therefore, the maximum voltage in all-cell initializing operation cannot be sufficiently reduced.
[Patent document 1] Japanese Patent Unexamined Publication No. 2000-242224